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post #9 of (permalink) Old 6th May 2008
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Fan resistor failure

Here are 2 ways to repair it WITHOUT removing the top facia, which is very difficult and for a lot less parts cost . At least they work on a Scenic II and the instructions below are for the Scenic II only, but the Scenic I is fairly similar

Method 1

Remove the heater switch and splice in behind it 4 wires of same thickness as existing wires to the position 1, 2, 3, 4 fan position outputs. You can cut them and leave the bit between the switch and resistor open circuit but probably best not to as that stops you replacing the real resistor at a later stage if you want to. Thread these new wires over the top of steering column to the dead space above the pedals (remove the lower facia which is much easier than the top facia.) Buy three 50 -100 watt metal clad resistors. (Cost 2 -3 each). Attach these with self tapping screws to a suitable heatsink using some heatsink compound. Wire these in as per your original resistor, i.e. all in series with the 4 wires tapping in at ends and in middle. Take care that no shorts to earth can happen, although the consequences of this are not too drastic as the fan just goes to full speed. But any sparking could ignite something. Strap up the wires well to make sure that, should the solder joints fail, there are no loose wires flapping about. Hang the heatsink with tiewraps over the cross-member and make sure it can not touch anything that will melt under the modest temperature the heatsink gets to. Make the fins on the heatsink run vertically to improve heat transfer to the air.

The downside of this is that it gets very hot if you get the installation wrong (as the resistors generate around 50W of heat; none on position 4) and I take no responsibility if your car catches fire or the resistors burn out. In the Renault resistor the fan cools it, I assume, as it's mounted in a fan duct.

I can confirm that if you use resistors of inadequate wattage or an inadequate heat sink then you will get smoke coming from them as happened to my prototype which I made for zero cost with gash components. Rather disconcerting to having smoke coming out of dashboard when driving down the motorway. But once I replaced them with the correct resistors/heatsink all was well.

Method 2.

Much more elegant it to use a PWM (Pulse Width Modulated) circuit as generates only 1-2W of waste heat. This is basically like a mains lamp dimmer but for 12V.

But have yet to work out how to translate the switches into a signal to set the right speed on the controller.

Both these require more electrical/electronic knowledge than the original repair. I***8216;d consider making up kits for say 50 for either of these, which takes out most of the difficulty for you. All you need to do is make the connections into the switch. It saves you the big job of taking off the facia and for the second option is more energy efficient as saves wasting 50W all the time the fan is on but not on high speed.

On the Scenic II it has been found that connector to the original resistor does not take the current involved and burns out. Renault has issued a modified loom that you need to install instead of the original. There is a serious risk your new resistor will quickly fail if you don***8217;t fit the new loom. This loom plus the resistor costs 100. Neither of the above mods needs this new loom as they don***8217;t use the original connectors.

My brother***8217;s new resistor on his Scenic 1 failed after one month so I wonder if that has the same loom problem. The quick fix of replacing the thermal fuse as reported on another post here, is not going to last long if the Scenic I also has a connector problem.

Sorry Renault if this post kills your resistor spares business but its your poor design that is causing these resistors to fail.
Currently in echase's garage:
04 Scenic 1.9dci

Last edited by echase; 8th August 2008 at 10:30 AM. Reason: typos
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